If small radii are to be produced in edge and corner regions of workpieces by means of internal high pressure forming, i.e. forming by means of pressurizing the workpieces with a high liquid pressure in suitable forming dies, then for shaping these small radii extremely high pressures of about 4000 bar and higher are necessary. Thus, for keeping closed the die parts and/or a surrounding pressure casing, particularly in the case of large-surface area parts, very high keeping closed forces are necessary, which are difficult to achieve. This more particularly applies in conventional internal high pressure forming, in which the die simultaneously constitutes the pressure enclosure for the liquid bringing about forming. The invention more particularly relates to blanks preformed by means of internal high pressure forming and is in particular part of a corresponding method. However, it can also be used for otherwise preformed blanks.
Thus, the problem of the invention is to provide a method and an apparatus by means of which a postforming of blanks can take place in critical edge and corner regions.